(1) Field of the Invention
The present invention relates to oxygen sensors and more specifically to a device for detecting the concentration of oxygen or a combustible constituent in gases utilizing an oxygen pump by means of a solid electrolyte body--i.e.) so-called oxygen sensor in a broad meaning.
(2) Description of the Prior Art
In the prior art, measurement of oxygen concentration in gases, particularly electric measurement, is performed by devices in which a cathode surface that is one electrode surface of a solid electrolyte oxygen pump element is sealed. A wall to seal the cathode surface is provided with fine diffusion holes (hereinafter referred to as "fine holes"), and oxygen in gases to be measured is introduced through the fine holes by means of diffusion phenomenon. At the same time the amount of current caused to flow by applying a prescribed voltage to both electrode surfaces is measured. The oxygen concentration in the gases is calculated from the measured current flow as disclosed in so-called diffusion limiting current measuring method (Japanese published unexamined patent application No. Sho 52-72286, Toyota Chuo Kenkyusho; Japanese published unexamined patent application No. Sho 53-66292, Westinghouse "Combustible Substance Sensor").
On the other hand, Japanese published unexamined patent application No. Sho 58-153155 proposes an oxygen sensor having an excellent response property where a narrow gap is formed in a pumping surface of an oxygen pump element, and an oxygen concentration cell element as an oxygen gas shielding body is arranged in opposition thereto. Limitation of the diffusion motion of the oxygen gas caused by the pumping of the oxygen pump element is effected by an open and edge portion of the narrow gap. In these oxygen sensors, however, since a pumping power source applied between the electrodes of the oxygen pump element and a heater power source to heat a sensor are separately installed, the device becomes complicated and expensive.